Granular superphosphate with low fluorine content



Patented July 8, 1941 or-"Flea GRANULAR SUPERPHOSPHATE wrrn LOW rwonmn CONTENT Mark Shoeld, Baltimore,,Md., assignor to The f Davison Chemical Corporation, Baltimore,

Application June 15, 1938, Serial No. 213,929

12Claims. (c1. 71-48) :My invention relates to an improved'type of granular 'superphosphate, and to a method of making the same.

Ordinary den superphosphate and granular superphos'phate made in a closed container have a relatively-high percent of fluorinein the final product. This fluorine is of great disadvantage in the industry, since it causes bag rot, and is otherwise undesirable. Bag rot causes the bags in which the superphosphate is shipped to rot and beneficial effect upon the setting qualities of'the I product either by itself, or. in admixture-with other materials. 1

In general my process consists in forming a granular superphosphate from den superphos- .phate. Preferably I employ fresh den superphosphate, but cured, or partially cured, den superphosphate may be employed. The starting, ma-

1 terial is conditioned by subjecting it to agglomeration in the presence of moisture and the agglomerated particles are then dried while agitating them, such as in a rotary direct heat dryer. Thisprocess results in hard, dry',,indurated and encrusted granules, which are several times the crushing strength of ordinary den superphos-' phate. It has been found that the drying step should be carried to a point that the superphosphate contains approximately 3 to 8 percent moisture. While the drying step is in progress, the hot gases are caused to flow over the granules while tumbling in the rotary dryer. The process is so regulated that when the desired moisture content is obtained the fluorine in the Figure 3 is a cross sectional view of the nodule shown in Figure 2. I

' Referring to the drawings, I have shown that I may employ a fresh, cured, or partially cured den superphosphate. Ordinarily it is more'economical to employ a fresh den superphosphate for the process. A cured, or partially cured super-- phosphate, however, may be granulated if desired. The starting material has mixed with it final product has been greatly reduced. The heat I and the volume of hot gases are so regulated that over 30 percent of the original fiuorinecontent of therock is eliminated, while the moisture is reduced to between the limits of 3 to 8 percent. The granular s'uperphosphate is then stored and allowed to cure to obtain a material of high available P205 with-low fluorine content.

In the drawings: I Figure 1 is a fiow sheet illustrating diagrammatically my process;

Figure 2 is a nodule of the granular super'phosphate; and

a finely divided dry material in the conditioning step. This dry material may be for instance sand or "fully cured den superphosphate, or ground phosphate rock, or classifier dust. Classifier dust is obtained by removing the dust from thestep of classification of the nodule sizes. The larger lumps may be broken and subjected to classification by means of screening or otherwiselto get the final productof the desired fineness, which is kept substantially uniform in order to insure its free flowing qualities when applied to theland. 'I'he fine dust which is collected from this classiffying process can be returned to the process mixed with, for instance, the fresh den superphosphate. g

- Water is added to the mixture of the starting material, such as fresh den super, and the dry finely divided material, such as the classifier dust.

"This conditioning stage is one in which agglomerated particles are formed, which are subsequently dried in the drying step. Ordinarily the conditioning step is carried out in a rotary drum.

In actual practice the contents of the drum may be inspected by an operator who regulates the amount of water which is introduced at' this stage through sprays directed inside the drum. By means of abeam of light thrown on the material in the drum, the operator can estimate accurately the amount of water which should be added to produce agglomerated particles ofsubstantially the desired uniform size.

From the agglomeration step the material is then passed to the drying step where, under agi, tation; the moisture in the agglomerated material is reduced and the fluorine content is reduced to a desired minimum.

Ordinarily the amount of water. which the agglomerated particles should lose in their passage maintain the moisturebetween the limitsof a to 5 ,5 percent in the product from the dryer.

When such moisture limits are maintained as above specified. danger of reversion of the available P205 is eliminated in the storage of the granular material. In fact, if proper moisture limits are maintained, there is an actual accelerated curing of the granules under storage so that within a relatively short time there is obtained a high percent of available P205. Some curing of course occurs in the passage of the granules through the dryer.

The regulation of the moisture in the dryer is, therefore, an important factor since it controls the curing rate in the dryer and the curing rate in storage after the dryer. Together with this moisture elimination, it is very necessary to maintain a temperature of the drying gases and a volume control of the drying gases such that,

by the time the granules have arrived at the desired minimum moisture content, they shall be ready to leave the drying step. This regulation of temperature of the gases and their volumetric motion over the drying particles should be such as to insure that over 35 percent of the original fluorine content is eliminated at the end of the dryingcyc'le. This may be stated in another way by stating that on the basis of percent of total P205 the fluorine content should be reduced to approximately 1.1 percent to 1.45 percent, when the final desired "moisture content has been reached at the end of the drying step.

The operation of the fluorine basis of computation will now be explained.

The fluorine content of the superphosphate of I course comes from the phosphate rock. By far the most important phosphate rock used for superphosphate manufacture in the United States is Florida rock, The fluorine content of this rock does not vary very much. A typical example is the following analysis: 33.4% P205 and 3.74% F. The superphosphate examples to be given later on are manufactured from this rock.

To be able to better visualize the relative fluorine content of the various materials, it is best to reduce them all to a common basis. 'For this purpose we will use the fluorine percentage, basis 20% total P205. The composition of the phosphate rock cited above may thus be expressed 2.24% F, basis 20%. P205, alternately it may be expressed as F:P2O5 ratio being 112/ 1000.

The reason for'this procedure is that superphosphates may have varying compositions as to moisture and total P205. The P205 being nonvolatile serves as an excellent reference point and the above statement is really an expression of the fluorine content as a function of the total P205 content.

Typical granular superphosphate made in a closed container from the Florida rock, as disclosed in Reissue Patent No. 19,825, has the following composition: 19.9% total P205 and 1.88%

F. 0n the basis of 20% total P205, the fluorine content is 1.90%, the FzP205 ratio being 85/1000. The fraction of the fluorine eliminated during the closed container method of manufacture is therefore:

This means that 15.2% of the fluorine originally present in the rock has been eliminated.

Granular superphosphate made by the present process'irom the Florida rock analyzes as follows: 21.45% total P205 and 1.40% F. 0n the basis of 20% total P205, the fluorine content is 1.30%, the F:P205 ratio being 65/1000.

The fraction of. the fluorine eliminated during the granular super manufacture is therefore:

This means that 42% of the fluorine originally present in the rock has been eliminated.

Tabulating the above, the result is as follows:

The effect of the above startling difference between the two kinds of granular superphosphate is fully borne out by actual practical experience as to bag rot and set.

In classifying the nodules there are some nodules over size, and these are crushed and the crushed material classified. As previously explained, the dust from the classifying step can be returned to the conditioning step where the agglomeration of the particles occurs.

.I desire that the invention be limited only by the scope of the appended claims and the showing of the prior art.

I claim:

1. A granular superphosphate fertilizer com prising nodular, gioboid, encrusted and indurated particles sufficiently coarse for distribution on the land without substantial dusting, but of a size to permit free flowing, in which the fluorine content is over 35 percent less than the fluorine content of the original rock from which the superphosphate is made, the fluorine content lying between 1.1 percent and 1.30 percent on the basis of 20 percent total P205.

2. A granular superphosphate fertilizer comprising nodular, globoid, encrusted and indurated particles sufliciently coarse for distribution on the land without substantial dusting but of a size to permit free flowing, in which the fluorine content lies between 1.1 per cent and 1.30 percent on the basis of 20 percent total P205.

3. A granular superphosphate fertilizer comprising nodular, globoid, encrusted and indurated particles sufliciently coarse for distribution on the land without substantial dusting but of a size to permit free flowing, in which the fluorine content is approximately 40 percent less than that of the original phosphate rock, the fluorine content being less than that of ordinary den superphosphate and lying between 1.1 percent and 1.30 percent on the basis of 20 percent P205.

4. A granular superphosphate fertilizer comprising nodular, gioboid, encrusted and indurated particles sufficiently coarse for distribution on the land without substantial dusting butof a size to permit free flowing, in which the fluorine content is under 1.30 percent on the basis of 20 percent P205.

5. A granular superphosphate fertilizer comprising nodular, globoid, encrusted and lndurated particles sufliciently coarse for, distribution on the land without substantial dusting but of a size to permit free flowing. inwhich the fluorine content is over 35 percent less than the, fluorine content of the original rock from which the superphosphate is made, the fluorine content being less than that of ordinary den superphosphate, lying between 1.1 percent and 1.30 percent on the basis of 20 percent total P205, and in which the crushing strength of the nodules is several .that of ordinary den superphosphate lying be tween 1.1 per cent and 1.30 percent on the basis times greater than the crushing strength of fully I cured den superposphate,

6. A granular superphosphate fertilizer comprising noduiar, globoid, encrust'ed and indurated particles sufliciently coarse for distribution on the land without substantial dusting but of a size to permit free flowing, in which the fluorine content lies between 1.15 percent and 1.30 percent on the basis of 20 percent total P205 and in which the crushing strength of the nodules is several times greater than the crushing strength of fully cured den superphosphate.

7. A granular superphosphate fertilizer comprising nodular, globoid, encrusted and indurated particles sufliciently coarse for distribution on the land without substantial dusting but of a size to permit free flowing, in which the fluorine content'is approximately 40 percent less than that of the original phosphate rock, the fluorine content being less than that of ordinary den superphosphate, lying between 1.1 percent and 1.30 percent on the basis or 20 percent P205, and

in which the crushing strength of the nodules is several times greater than the crushing strength of fully cured den superphosphate.

8. A granular superphosphate fertilizer comprising nodular, globoid, encrusted and indurated particles sufliciently coarse for distribution on the land without substantial dusting but of a size to permit free flowing, in which the fluorine content is under 1.30 percent on the basis of 20 percent total P205, and in which the crushing strength or the nodules is several times greater than the crushing strength of fully cured den superphosphate.

9. As a new product, a superphosphate tertilizer in porous, discrete particles sumciently of 20 percent total P205, formed by crushing the product of claim 1.

10. As a new product, a superphosphate fertilizer comprising porous, discrete particles sufficiently coarse for distribution on the land without substantial dusting but of a size to permit free flowing, having a crushing strength several times greater than the crushing strength of fully cured den superphosphate in which the fluorine content is under 1.30 percent on the basis of 20 percent total P205 formed by crushing the product or claim 8. 11. As a new product, a granular superphosphate fertilizer low in fluorine content and possessing non-bag rotating and non-setting properties obtained by mixing den superphosphate and finely divided material, agglomerating the mixture in the presence of moisture and drying the granules until the fertilizer contains approximately 4 to 6 percent moisture, the product being nodular, globoid, encrusted, and indurated particles suiflciently coarse for distribution on the land without substantial dusting but oi. a size to permit tree flowing, in which the fluorine content lies between 1.1 percent and 1.30 percent on the basis of 20 percent total P205.

12. As a new product, a granular superphosphate fertilizer low in fluorine content obtained by agglomerating den superphosphate in the presence oi moisture and drying the granules until the fertilizer contains approximately 4 to 6 percent moisture, and the fluorine content being less than the fluorine content of the den superphosphate lying between 1.1 percent and 1.30 percent on the basis or 20 percent P205, the product being nodular, globoid. encrusted and indurated particles sumciently coarse for distribution on the land without substantial dusting but of a size to permit tree flowing, and the crushing strength of the nodules being several times greater than the crushing strength or cured den superphosphate.

MARK SHOELD.

t CERTIFICATE OF conmacmon. Patent No. 2,2 3, 11 July 19in.

MARK SHOELD.

Itis hereby certified that error appears in the printed specificatioh of the above numbered patentrequiring correction as follows: Page 5, second celumn, line '19, claim 11, for the word "rotating" read --rott1ng--;

end that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 9th day of September, A. D. 191L1- Henry van Aradale, (Seal) Acting Commissioner e1 Patents. 

